Spark plug



Dec. 21, 1926.

1,611,856 G. W. FARNSWORTH SPARK PLUG Filed April 2, 1923 A ,h'u%s\\\ 4 fizvenarn J/Lorzzey. m Wu Patented Dec. 21, 1926. 1,511,855

UNITED STATES PATENT OFFICE.

GEORGE VI. FARNSWORTH, OF StN FRANCISCO. CALIFORNIA, ASSIGNOR TO 0. A. LINDSTROM. OF SAN FRANCISCO, CALIFORNIA.

SPARK PLUG.

Application filed April 2, 1923. Serial No. 629.284.

This invention ielates particularly to a modified term of spark plug for internal comlnistion engines.

The principal object of this invention is to provide a disk protector, constructed of heattcstcd metal, formed integrally with the shell casing for shielding the terininals of the electrodes adjacent the spark gap, thus preventing oil vapor and the waste carbon dets of con'ilnistion from collecting on the electrode terminals.

.3 further object of this invention is to reduce the exposed area of porcelain within the cylinder to the minimunn consistent with good insulation. Another object contemplates a new and novel construction of an insulating block positioned within the retaining shell so that the same may be removed therelron'i without removing the shell i'rom its position in the cylinder wall. A still further object is to provide a two part insulating member of which the exposed portion will be constructed of durable material not easily broken.

in this specification and the annexed drawings, the invention is illustrated in the form (:{lllSlClQl'Qh to be the best, but it is to be understood that the invention is not limited to such form, because it may be embodied in other terms; and it is also to be understood that in and by the claim following the de srription, it is desired to cover the inven tion in whatsoever form it may be embodied.

In the accompanying one sheet of drawings.

F 1 illustrates a sectional elevation through a spark plug constructed in accordance with my invention.

Fig. 9 is a bottom plan view of the same.

In detail the construction illustrated in the drawings includes the outer enclosing shell 1. ol? the spark plug, comprising a substantially cylindrical body of metal, having an annular shoulder 2 thereon for wrench engagement, and provided with an externally threaded stem 3, adapted to engage a spark plug socket in the wall 4 of an internal combustion engine. The shell is provided with an annular internally extended shouhlcr 5 adjacent the threaded huh 3, narrowing the inner diameter 5 of the shell .1. at this extremity. Contiguous to the orilice 5' the shoulder 5 is provided with an outwardly extending arm 6 terminating in a substantially annular disc 7 at right angles to the projecting arm (3, and having its radial center approximately in alinemcnt with the vertical axis through the center of the cylindrical shell 1.

The opposite end of the shell 1 is internally threaded at S for engagement with the exteriorly threaded retaining bushing 5) provided with a shoulder 10 for wrench en gageinent. The insulation comprises a sew tional n'iember consisting preferably of a porcelain core 11, adapted to extend with in the explosion chamber of the cylinder and an exposed fiber. refractory, or other heat resisting and non-conducting member 12.

The porcelain member 11 substantially cylindrical in cross section is provided with an annular reduced end 13 extending through the opening 5 leaving the shoulder abutting against the asbestos or heat resisting gasket 15, interposed between it and the shoulder 5 permitting expansion or contraction of the metallic shell relative to the porcelain 11 and preventing shocks or strains being transmitted to the porcelain. The insulating head 12 forms a flush joint connection with the porcelain 11 and the body portion thereof is reduced at 16, leaving the shoulder 17 adapted to be engaged by the inner end of the bushing 9. The reduced part of the insulating stem 16 fits snugly within the opening provided in the bushing 9 and is thus substantially alined on the vertical axis of the cylindrical shell 1. The inner face of the bushing 9, contacting with the shoulder 17, provides a ready means of adjustment for tightly holding the member 12, against the porcelain 11 in position within the shell.

The conducting electrode 20 is concentrically located within the porcelain 11 and has its inner end projecting through the an nular extension 13 terminating in the usual firing joint 18. Adjacent the connection between porcelain 11 and the insulating head 12, the conducting rod 20 has a circular plate 21 secured thereon and resting with an annular depression formed in the porcelain. The electrode 20 is contained concentrically through the fiber or non-conducting head 12 and tern'iii'iates in a threaded end 22 provided with a binding nut 23 threaded thereon.

The shield disc is provided with an upwardly projecting electrode 19 on its inner face, positioned in axial alinement with the electrode 20, concentrically located within the porcelain 12. The reduced end 13 of the porcelain ll snugly engages the opening 0 in the shell 1 through whlch 11; passes minimizing the exposed surface upon which carbon deposits may collect.

An integrally formed disc protector such as described when placed anterior to and shielding the firing points, efiectively prevents the oil vapor from condensing on the electrode terminals, which under ordinary conditions are exposed to the explosion of the carburetted air and provide a surface upon which the waste products of combustion can be deposited; such carbon deposits are detrimental to the efficient operation of the plug, since sufficient carbon deposits are better conductors than the air gap between the main and ground electrodes. In the present construction the exposed area oil terminal points is reduced to the mini mum, consistent with good electrical action. The shield 7 protects the terminals by creating an isolated electrical zone of electrical discharge between the terminals, that has a disrupting eii'ect upon carbon deposits before their mass can build up to a point of conductivity greater than the spark gap.

Having thus described this invention, what I claim and desire to secure by Letters Patent is In a spark plug, a shell having an apertured bottom; an insulating member er.- gaging the apertured bottom of the shell and having a reduced extension which projects through the aperture; a main electrode in the insulating member having one end projecting therebeyond; an arm integral with the shell; a shield integral with the arm and extending over said end of the main electrode; and a point extending upwardly from the inner face of the shield and alined with the end of the main electrode.

In testimony whereof, I have hereunto set my hand at San Francisco, California, this 19th day of March, 1920.

GEORGE w. FARNSWORTH. 

